1. Field of the Invention:
This invention relates to a dental treatment with a dental composition adapted to improve the bond between the tooth and a dental filling meterial. In a further aspect, the invention relates to a dental composition for assuring an improved bond between the tooth and a filling material such as a composite resin, a pit and fissure sealant, a cementing agent or the like which is used in the treatment of caries, for instance.
2. Description of the Related Art:
In the treatment of dental caries, it is common practice to pretreat the enamel of the affected tooth with an aqueous acid solution for assuring a firm bond between the tooth and an organic material (e.g. composite resin, glass ionomer cement, carboxylate cement, composite resin cement, and pit and fissure sealant). As such an enamel treating agent, an aqueous solution of phosphoric acid or citric acid has heretofore been employed widely and from the standpoint of effectiveness, an aqueous solution containing 20 to 60 percent by weight of phosphoric acid has been recommended.
The composite resin used in the restorative filling of the carious portion of a tooth, which consists of a synthetic resin and an inorganic filler, has only a poor adhesive ability for the tooth and much research has been undertaken for improving the adhering power. The effective restorative procedure heretofore known for dental caries comprises removing the carious part of the tooth, etching the enamel wall of the resulting cavity with an aqueous acid solution (e.g. an aqueous solution of phosphoric acid), then applying an adhesive containing a polymerizable monomer which is a component of a composite resin and finally filling the cavity with the composite resin. However, since the tooth comprises enamel and dentin and the cavity formed by removal of a carious portion has exposed walls of both enamel and dentin, it is desirable that the composite resin be able to firmly bond to both enamel and dentin. For this reason, the recent practice exploits adhesives containing a special polymerizable monomer having an affinity for dentin.
When the carious tooth is cut with burs, a smeared layer is formed on the cut surface. It is believed that this smeared layer includes the bacteria derived from the caries and those resident in the oral cavity. If a restorative procedure with a composite resin is performed with the smeared layer as it is, the composite resin will separate from the smeared layer because the smeared layer is brittle. Moreover, the irritating effect which the bacteria included in the smeared layer exerts on the dental pulp may also be a serious concern. Therefore, the smeared layer is preferably removed before the restorative procedure using a composite resin is actually undertaken.
If the whole surface of the burred cavity is treated with an aqueous solution of phosphoric acid, the smeared layer on the enamel and dentin will be completely removed but the dentinal tubules plugged by the smeared layer will then be exposed and irritant substances may easily reach the pulp through the tubules to cause undesirable effects. Therefore, attempts were made to use various organic carboxylic acids, in lieu of phosphoric acid, for the pretreatment of the dentin. It has been reported that the use of an aqueous solution of citric acid, oxalic acid or formic acid and/or a metal salt such as ferric oxalate, ferric chloride or the like was effective for the aforementioned purpose (e.g. Nakabayashi et al., Journal of the Japan Society for Dental Apparatus and Materials, 23, 61, 29-33, 1982). However, even when the enamel is pretreated with such a known agent, the bond between the composite resin and the enamel is not as good as that attainable by using an aqueous solution of phosphoric acid. Therefore, it is generally necessary to first pretreat the dentin with an organic carboxylic acid or the like and then pretreat the enamel with an aqueous solution of phosphoric acid, thus adding to the complexity of the restorative procedure.
Thus, while the dental treating agents containing oprganic carboxylic acids are effective for dentin, they are not so effective for enamel and, therefore, the enamel must be subsequently treated with an aqueous solution of phosporic acid, thus adding to the complexity of the clinical procedure as mentioned just above. Thus, organic carboxylic acids are not universally suited for the treatment of all classes of dental caries.
Although the most important function which a dental treating agent is expected to perform is an enhancement of the bond strength between the filling material and the enamel and dentin, it is also important that such an agent have little denaturation effect on the dentin, particularly on its collagen.